1. Field of the Invention
This invention pertains generally to communication networks and, more particularly, to wireless communication networks including a network coordinator. The invention also pertains to data aggregation methods for wireless communication networks.
2. Background Information
Wireless communication networks are an emerging new technology, which allows users to access information and services electronically, regardless of their geographic position.
All nodes in ad-hoc wireless communication networks are potentially mobile and can be connected dynamically in an arbitrary manner. All nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes in the network. For example, ad-hoc wireless communication networks are very useful in emergency search-and-rescue operations, meetings or conventions in which persons wish to quickly share information, and in data acquisition operations in inhospitable terrains.
An ad-hoc mobile wireless communication network comprises a plurality of mobile nodes, each of which is able to directly communicate with its neighboring mobile nodes, which are a single hop away. In such a network, each mobile node acts as a router forwarding packets of information from one mobile node to another. These mobile nodes communicate with each other over a wireless media, typically without any infra-structured (or wired) network component support.
In contrast to wired networks, mesh-type, low rate-wireless personal area network (LR-WPAN) wireless communication networks are intended to be relatively low power, to be self-configuring, and to not require any communication infrastructure (e.g., wires) other than power sources.
During radio frequency communication between a network coordinator and one or more network devices, communications may be hindered or interrupted by one or more sources of background noise at various frequencies. One known method of dealing with such background noise is for the network coordinator to configure its radio (i.e., a wireless transceiver) to leave the present wireless channel (i.e., a first radio frequency band), to scan other wireless channels (i.e., other radio frequency bands) with that same radio, and to return to the present wireless channel and use the radio to notify the network devices to migrate to a new wireless channel (i.e., one of the other radio frequency bands).
In a large scale wireless lighting application, after the ballasts receive a broadcast command from a node, such as a network coordinator (e.g., iZAP™ marketed by Eaton Electrical, Inc. of Milwaukee, Wis.), the individual status (e.g., without limitation, on; off; light level; mains energy) of each ballast needs to be sent back to that node as fast as possible (e.g., ideally, below 1 second; below 5 seconds). There may be up to about 500 or more ballasts. A link between a ballast and the network coordinator may potentially interfere with another link between another ballast and the network coordinator if the same channel is used.
One prior proposal is Carrier Sense Multiple Access (CSMA), which is a probabilistic Media Access Control (MAC) protocol in which a node verifies the absence of other communication traffic before transmitting. The node's transceiver listens for a carrier wave before trying to send. In other words, it tries to detect the presence of a signal from another node before attempting to transmit. If a carrier is sensed, then the node waits for the transmission in progress to finish before initiating its own transmission. Of course, multiple different nodes send and receive on the same medium, and transmissions by one node are generally received by all or a number of other nodes using the same medium. Hence, CSMA causes unnecessary collisions and, therefore, is too slow.
Time Division Multiple Access (TDMA) is a channel access method for shared medium (usually radio) networks. It allows several users (nodes) to share the same frequency channel by dividing the signal into different time slots. The nodes transmit in rapid succession, one after the other, each using its own time slot. This allows multiple nodes to share the same transmission medium (e.g., radio frequency channel), while using only the part of its bandwidth that they require.
TDMA is used, for example, in the digital 2G cellular systems, such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, and combat-net radio systems.
The TDMA frame structure includes a data stream divided into frames and those frames are divided into time slots. TDMA is a type of time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile telephone to a base station, this becomes particularly difficult because the mobile telephone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.
There is room for improvement in wireless communication networks.
There is also room for improvement in data aggregation methods for wireless communication networks.